HARARE — Two of Zimbabwean President Robert Mugabe's chief rivals said on Wednesday they were allying to deny the 93-year-old another term in office.

Morgan Tsvangirai, 65, who was Zimbabwe's prime minister in an uneasy coalition government with Mugabe from 2009 until 2013, said he and Joice Mujuru, who was Mugabe's vice president for a decade until she was fired in 2014, would seek to form a coalition government to bring political change.

"This is just the beginning of the building blocks toward establishing a broad alliance to confront ZANU PF between now and the next election in 2018," Tsvangirai said, referring to the party led by Africa's oldest leader.

Mugabe, one of the last of the generation of African nationalists that sough the overthrow of white colonialists, has run Zimbabwe since 1980. He was first prime minister then, in 1987, became president.

In December his ZANU PF party confirmed him as its candidate for the next presidential election expected in mid-2018, when he will be 94.

Tsvangirai, a three time loser to Mugabe, said he expected similar deals to the one with Mujuru would be struck with other political groups.

Tsvangirai, who lost the 2013 presidential vote against Mugabe, is now leading MDC-T, a faction of the Movement for Democratic Change, that was formed after the party was weakened by splits over how to confront Mugabe.

The MDC, evicted from the unity government after its crushing defeat in the 2013 election, has been split over whether to dump Tsvangirai before the next vote in 2018.

Mujuru, who formed a new National People's Party in March last year, said the two parties had worked on the agreement for the last six months and would now start negotiating specific details to strengthen their alliance.

Critics accuse Mugabe of wrecking one of Africa's most promising economies through policies such as violent seizures of white-owned commercial farms and money printing. He and his party say the economy has been undermined by western powers.

The turmoil within the opposition has been a boost for Mugabe, whose party has ruled Zimbabwe since independence from Britain in 1980 amid charges of rigging recent elections. Mugabe has rejected the claims.

The southern African nation's economy stagnated last year following a devastating drought while its budget deficit exploded as Mugabe's administration struggled to pay its workers, which helped fan anti-government protests.